Chuck DeMilo Director, Product Marketing
Luminus Devices, Inc. 1100 Technology Park Dr.,
Billerica, MA 01821
LED Performance & Testing
Bigger chips (fewer LEDs)
1mm2 2mm2
100+ lm 200+ lm
4mm2
400+ lm
9mm2
900+ lm
Fewer LEDs but with the same fixture lumens and efficacy
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Kilo-lumen LEDs
Current density (A/mm2)
Rel
ativ
e Ef
fica
cy (
LPW
)
80%
90%
100%
110%
120%
130%
140%
150%
0.00 0.25 0.50 0.75 1.00
350mA/mm2 1mm2 = 350mA 2mm2 = 700mA 9mm2 = 3150mA
Bigger chips produce high lumen solutions with high efficacy
1mm2 2mm2
9mm2
100+ lm 200+ lm
900+ lm
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Thermal Flux Density
Spatially separated sources with distributed thermal flux
Single source with higher thermal flux density
Thermal management is critical to ensure reliability of high flux density sources
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Thermal Management
0%
20%
40%
60%
80%
100%
25 50 75 100 125 150Junction Temperature (C)
Rel
ativ
e Lu
min
ous
Flux
(%)
Flux vs. Junction Temp (typical) Life vs. Junction Temp (typical)
0%
20%
40%
60%
80%
100%
75 100 125 150Junction Temperature (C)
Rel
ativ
e Li
fetim
e (L
70/B
50)
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Chip Construction: Thermal Optimization Chip construction
– Vertical chip design – High External Quantum Efficiency – Current (heat) spreading electrodes – Epitaxial layer bonded to metal sub-mount
LED junction
Metal substrate
Current spreading electrodes
Surface extraction
High efficiency back reflector
Sub-mount material Thermal Conductivity (W/mK)
Sapphire 35
Silicon 150
Copper Tungsten 200
Copper 350
LED chip design for high optical & thermal flux density 8
Aluminum Nitride Ceramic
Material Thermal Conductivity (W/mK)
Aluminum Nitride 200
Aluminum Oxide 20
LED package design for high optical & thermal flux density
Package Construction: Thermal Optimization
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LM-79 Electrical & Photometric Measurements of
Solid-State Lighting Products
Tests • Voltage & Current • Luminous Flux • Luminous Efficacy • Intensity vs. Angle • Color (CCT & CRI)
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LM-82 Characterization of LED Light Engines & LED Lamps for Electrical and
Photometric Properties as a Function of Temperature
Zhaga: An LED light engine is a combination of an LED module and the associated control gear.
Test at multiple temperatures • Current & Voltage • Luminous Flux • Luminous Efficacy • Intensity vs. Angle • Color (CCT & CRI)
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LM-80 Measurement of Lumen Maintenance of
LED Light Sources
Test at multiple temperatures vs. time • Current & Voltage • Luminous Flux • Chromaticity
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LM-80 Test Requirements • Testing at a NVLAP 17025 accredited laboratory.
– Technical qualifications and competence
• Control parameters – Junction temp – Ambient air temp – Relative humidity
• Duration – Minimum 6,000 hours – Measurement interval of 1,000 hours
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Temperatures & Measurement Points • LM-80 requires 3 case temperatures (Ts) 55°C, 85°C and 3rd temp determined by LED manufacturer
________________________________
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Test Conditions
• Current: 3.2A = 350mA/mm2 • Ambient air temp (TA): TA maintained within 5°C of TS
• Relative Humidity: RH < 65%
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LM-80 Test Data
Increase in light output? • Diffusion of dopants • Relaxation of internal stresses
Short-term artifact, brightness will not continue to increase over time 19
TM-21 Projecting Long Term Lumen Maintenance of
LED Light Sources
• Max lumen maintenance projected life = 6X test duration.
• Sample size ≥ 20 units per test condition to use the 6X multiplier.
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Lumen Maintenance Calculation Average Degradation
Understand the performance of the all of the LEDs under test!
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Failure Modes “LM-80 does not attempt to induce any failure modes”
LM-80 is a partial view into overall reliability and anticipated lifetime
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Test Methods: Wafers & Wafer Lots
• LM-80/TM-21 do not specify the number of wafers or wafer lots used for the test. – Testing 20 LEDs from 3 different wafer lots may be more
meaningful than testing 1,000 LEDs from a single wafer lot.
Test data should represent the production distribution
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Lumen Maintenance: B50 & B10
B50 = 50% of population fails at the L70 lifetime B10 = 10% of population fails at the L70 lifetime
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L70(B50) = 68,000 hours at Tj=110C at 9A L70(B10) = 21,000 hours at Tj=110C at 9A
• LED Manufacturer Testing Beyond LM-80 – Full Qualification Testing – Highly Accelerated Testing
• Induce Failure Modes
– Infant Mortality
Additional Reliability Analysis
Lumen Maintenance
Qualification Test Reports Reliability Application Notes
Data Sheets 29
Summary • LM-80 & TM-21 are critically important in
standardizing the lumen maintenance projections for LEDs and driving adoption.
• Luminaire manufacturers and municipalities should: – Dig into the LM-80 test methodology – Understand the distribution of performance (not just the average) – Go beyond LM-80 to fully understand reliability and expected lifetime
A comprehensive examination of all available reliability and lifetime data will lead to the best purchasing and deployment decisions.
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